<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
        <script>
            var arr=[21,12,1,3,4]
            
            var c=arr.sort((a,b)=>{
                return b-a;
            })
            console.log(c)   //[1,3,4,12,21]
        </script>
</body>
</html>